The present invention relates generally to the preparation of a water-impervious concrete structure and specifically to the economical preparation of roadways, bridge decks, concrete pipe, structural pilings, preformed structures and the like which are desired to be made water-impervious such that water and contained ions do not cause spalling, delamination or other deterioration of the concrete structure.
For example, corrosion of reinforcing steel caused by chlorides from de-icing salt, airborne ocean spray or the like is a major cause of premature deterioration of concrete highways and bridge decks. As rust builds up, the steel expands and cracks the concrete. In dealing with this problem, it has been common practice heretofore to seal the concrete by coating the surface with linseed oil or by adding to the standard Portland cement mixture a small amount of wax beads. In the latter instance, after the concrete has cured, the surface of the roadway or bridge deck is heated to melt the wax beads, thereby sealing the capillary passages normally formed in cured concrete. Beads used in the past have been a blend of paraffin and Montan wax, the Montan wax acting as a wetting agent to facilitate the migration of the wax blend into the capillaries and minute interstices of the cured concrete which are generated by fugitive water in excess of that required for cement hydration. Heating of the concrete surface has been ordinarily accomplished by the use of electric blankets or electric-or-gas-fired infra-red heaters. Since the melting point of the paraffin/Montan wax blend is in excess of 75.degree. C., the surface must be heated to at least 85.degree. C. and to as much as 212.degree. C. and to a depth of about two inches in order to insure complete migration of the wax into the capillaries and achieve concomitant internal sealing of the concrete structure.
Substantial problems exist with respect to the internal sealing methods and compositions heretofore employed. Due to the high temperature needed to cause migration of the paraffin/Montan wax composition, requisite equipment must be purchased, transported from work site to work site, and maintained, in order to complete the sealing of concrete surfaces, all at considerable expense. In addition, the high heat employed and resultant localized, differential thermal expansion may cause cracking of the adjoining unheated concrete unless suitable temperature gradients are established.
The present invention overcomes these problems and achieves other advantages not found in the prior art by the replacement of the Montan wax with animal byproducts, combining high wetting ability, low melting point, low melt viscosity, and low cost. Specifically, the advantages of the present invention include:
(1.) low total cost due to the low raw material cost and low labor and energy costs resulting from short heat-treating times and a comparatively low temperature necessary to effect complete sealing of the concrete;
(2.) improved sealing due to the complete chloride blockage;
(3.) improved strength due to the low additive concentration; and
(4.) a reduced danger of structural damage due to low thermal stress in heating and cooling.